It is often required to trace and identify a particular one or all of the electrical circuits within a building or other installation for purposes of repair, modification, or to determine whether additional load may be placed on the circuit. An exceedingly large number of branch circuits may exist within a particular installation, all emanating from an incoming multi-phase power source. Of course circuit identification is often no problem if adequate wiring diagrams exist, but as installations are modified, new branches added an old circuits extended, the identity of a circuit from the load back to the panel or feeder simply is unknown. Even documentation, when it does exist is frequently unreliable and experienced electrical engineers will insist that the wiring be traced at the site.
Circuit identification has traditionally been accomplished by disconnecting power from the group of circuits under investigation and tracing continuity of the particular branch by the introduction of a test signal at one end of the de-energized circuit while sensing for the test signal at the opposite end of the circuit to isolate the circuit being sought. According to one prior technique, the test signal input is an audio frequency voltage which is detected by headphones at the opposite circuit end. Each branch being identified is tested separately and since this may be a time consuming task, it is not uncommon for the power to be disconnected for considerable periods.
In many instances it is highly inconvenient and often impractical to de-energize the electric circuits under investigation. For example, in an electrical distribution system within a hospital, the removal of power will disrupt hospital operation and can be of serious consequence.
It is also undesirable to de-energize the electrical circuits in a computer center or in a continuous process installation wherein loss of power can produce ruinous results. Even in less critical electrical distribution systems such as in an office building, the shutdown of power can cause great inconvenience to tenants, and if such shutdown were to occur other than during usual working hours, as on weekends and holidays, additional expense can arise by reason of the payment of overtime wages to personnel involved. Thus, the advantages of being able to identify all circuits in a functioning installation without removal of power from such circuits is self-evident.